This application is a 371 of PCT/JP98/05398, filed Nov. 30, 1998.
1. Technical Field
The present invention relates to a process for producing a multi-layer printed wiring board, said process permitting mass production of a multi-layer printed wiring board with small-diameter via holes. Increased productivity is made possible, by driving the galvano head at a higher speed.
2. Background Art
A build-up multilayer wiring board alternately has interlayer resin insulators and conductive circuit layers, provides holes to the interlayer resin insulator layers, and then electrically connects the upper layers and lower layers by forming conductive films on the surface of the walls of these holes.
A hole (via hole) in the interlayer resin insulating layer is generally formed with the use of an exposure and developing process, which gives photosensitive property to the interlayer resin.
However, the required diameter of these via holes in a multilayer printed wiring board is almost 100 xcexcm or less, thus it is necessary to develop technology which makes it possible to maintain this small diameter. Due to such stringent requirements, the employment of a processing method utilizing a laser beam for the boring of the holes in the build-up multilayer wiring board will now be investigated.
Technology using laser for boring is proposed, in JPA HEI 3-54884. According to this method, a light beam from a laser source is received by a processing head for deflection. Thereby, the laser beam is irradiated to a predetermined resin insulator to form a hole.
In mass production of multi-layer printed wiring boards, which have hundreds to thousands of via holes in each layer, efficient hole drilling is essential. In addition, via holes need accurate positioning for electrical connection to conductor circuits in the layers below.
Unfortunately, it has been difficult to control, with high accuracy, the position of laser irradiation for via hole drilling in mass production. This has aroused a need for a process for fabricating a multi-layer printed wiring board containing openings at accurate positions. However, the current method of manufacture can not guarantee accurate positioning of laser irradiation. Improvement in positioning accuracy is offset by a necessary decrease in head driving speed, which in turn lowers productivity.
The present invention aims to address the above-mentioned problems. It is an object of the present invention to provide a process for producing a multi-layer printed wiring board, said process permitting accurate positioning of via holes independent of the accuracy of position for laser irradiation, thereby drilling a large number of holes efficiently by laser irradiation.
It is another object of the present invention to provide a method for increasing the driving speed of the scanning head without decreasing the accuracy of positions of via holes.
In order to achieve the aforementioned objectives, the present invention according to claim 1, provides a process for producing a multi-layer printed wiring board, which comprises the following steps (a) to (c).
(a) forming an interlayer insulating resin layer having a metal film, an opening formed on the metal film and a register mark on the surface thereof on a board covered with a conductor layer,
(b) removing that part of the interlayer insulating resin layer which is exposed through the opening in said metal film, by irradiation of a laser beam aimed at the opening according to data obtained by sensing the position of the register mark, thereby forming an opening through which a via hole is formed, and
(c) forming via holes and conductor circuits.
In order to achieve the invention""s objectives, the present invention according to claim 2, provides a process for producing a multi-layer printed wiring board, which comprises the following steps (a) to (c).
(a) forming an interlayer insulating resin layer on a board covered with a conductor layer,
(b) forming a metal film, an opening formed on the metal film and a register mark on the surface of said interlayer insulating resin layer, and
(c) removing that part of the interlayer insulating resin layer which is exposed through the opening in said metal film, by irradiation of a laser beam aimed at the opening according to data obtained by sensing the position of the register mark, thereby forming the opening through which a via hole is formed.
In order to achieve the invention""s objectives, the present invention according to claim 3, provides a process for producing a multi-layer printed wiring board, which comprises the following steps (a) to (d).
(a) placing a metal-clad resin film on a board covered with a conductor layer and performing hot-pressing, thereby forming an interlayer insulating resin layer having a metal film on the surface thereof,
(b) forming an opening and a register mark on said metal film,
(c) removing that part of the interlayer insulating resin layer which is exposed through the opening in said metal film, by irradiation of a laser beam aimed at the opening according to data obtained by sensing the position of the register mark, thereby forming the opening through which a via hole is formed, and
(d) forming a via hole and a conductor circuit.
In order to achieve the invention""s objectives, the present invention according to claim 4, provides a process for producing a multi-layer printed wiring board, which comprises the following steps (a) to (f).
(a) forming an interlayer insulating resin layer having a metal film, an opening formed on the metal film and a register mark on the surface thereof on a board covered with a conductor layer,
(b) removing that part of the interlayer insulating resin layer which is exposed through the opening in said metal film, by irradiation of a laser beam aimed at the opening according to data obtained by sensing the position of the register mark, thereby forming the opening through which a via hole is formed,
(c) forming a film by electroless plating on the board obtained in step (b) above,
(d) forming a plating resist on the board obtained in step (c) above,
(e) performing electrolytic plating on the part where said plating resist is not formed, and
(f) removing said plating resist and, removing by etching, the metal film and electrolessly plated film under the plating resist, thereby forming a via hole and a conductor circuit.
In order to achieve the invention""s objectives, the present invention according to claim 5, provides a process for producing a multi-layer printed wiring board, which comprises the following steps (a) to (h).
(a) forming an interlayer insulating resin layer on a board covered with a conductor layer,
(b) forming a metal film on the surface of the interlayer insulating resin layer,
(c) forming an opening and a register mark on said metal film,
(d) removing that part of the interlayer insulating resin layer which is exposed through the opening in said metal film, by irradiation of a laser beam aimed at the opening according to data obtained by sensing the position of the register mark, thereby forming the opening through which a via hole is formed,
(e) forming a film by electroless plating on the board obtained in step (d) above,
(f) forming a plating resist on the board obtained in step (e) above,
(g) performing electrolytic plating on the part where said plating resist is not formed, and
(h) removing said plating resist and, removing by etching, the metal film and electrolessly plated film under the plating resist.
In order to achieve the invention""s objectives, the present invention according to claim 6, provides a process for producing a multi-layer printed wiring board, which comprises the following steps (a) to (g).
(a) placing a metal-clad resin film on a board covered with a conductor layer and performing hot-pressing, thereby forming an interlayer insulating resin layer having a metal film on the surface thereof,
(b) forming an opening and a register mark on said metal film,
(c) removing that part of the interlayer insulating resin layer which is exposed through the opening in said metal film, by irradiation of a laser beam aimed at the opening according to data obtained by sensing the position of the register mark, thereby forming the opening through which a via hole is formed,
(d) forming a film by electroless plating on the board obtained in step (c) above,
(e) forming a plating resist on the board obtained in step (d) above,
(f) performing electrolytic plating on the part where said plating resist is not formed, and
(g) removing said plating resist and, removing by etching, the metal film and electrolessly plated film under the plating resist, thereby forming a via hole and a conductor circuit.
In order to achieve the invention""s objectives, the present invention, provides a process for producing a multi-layer printed wiring board, which comprises the following steps (a) to (c).
(a) forming an interlayer insulating resin layer having a metal film, openings formed on the metal film, and register marks on the surface thereof on a board covered with a conductor layer,
(b) placing said board with said register marks on a table of an apparatus for producing a multi-layer printed wiring board, said apparatus including; an emitter of fabricating laser, a scanning head to deflect the direction of the laser beam in X-Y directions, a camera to sense the register mark on the board, a table to support the board, an entry part for entrance of data for fabricating the board, a memory to store fabricating data or computed results, and an operation part, entering processing data into said apparatus,
sensing the position of the register mark on the board by means of the camera and comparing the results of sensing with previously entered processing data, thereby generating in the operation part, data necessary to drive the scanning head, the table, and storing the data in memory,
irradiating the openings in said metal film with a laser beam, with the scanning head and table controlled by the control part which reads the driving data from memory, thereby removing the interlayer resin layer and forming openings through which via holes are formed, and
(c) forming via holes and conductor circuits.
In order to achieve the invention""s objectives, the present invention, provides a process for producing a multi-layer printed wiring board, which comprises the following steps (a) to (c).
(a) forming an interlayer insulating resin layer on a board covered with a conductor layer,
(b) forming a metal film, openings formed on the metal film, and register marks on the surface of said interlayer insulating resin layer, and
(c) placing said board with said register marks on a table of an apparatus for producing a multi-layer printed wiring board, said apparatus including; an emitter of fabricating laser, a scanning head to deflect the direction of the laser beam in X-Y directions, a camera to sense the register mark on the board, a table to support the board, an entry part for entrance of data for fabricating the board, a memory to store fabricating data or computed results, and an operation part, entering processing data into said apparatus,
sensing the position of the register mark on the board by means of the camera and comparing the results of sensing with previously entered processing data, thereby generating in the operation part, data necessary to drive the scanning head, the table, and storing the data in memory,
irradiating the openings in said metal film with a laser beam, with the scanning head and table controlled by the control part which reads the driving data from memory, thereby removing the interlayer resin layer and forming openings through which via holes are formed.
In order to achieve the invention""s objectives, the present invention, provides a process for producing a multi-layer printed wiring board, which comprises the following steps (a) to (d).
(a) placing a metal-clad resin film on a board covered with a conductor layer and performing hot-pressing, thereby forming an interlayer insulating resin layer having a metal film on the surface thereof,
(b) forming openings and register marks on said metal film,
(c) placing said board with said register marks on a table of an apparatus for producing a multi-layer printed wiring board, said apparatus including; an emitter of fabricating laser, a scanning head to deflect the direction of the laser beam in X-Y directions, a camera to sense the register mark on the board, a table to support the board, an entry part for entrance of data for fabricating the board, a memory to store fabricating data or computed results, and an operation part, entering processing data into said apparatus,
sensing the position of the register mark on the board by means of the camera and comparing the results of sensing with previously entered processing data, thereby generating in the operation part, data necessary to drive the scanning head, the table, and storing the data in memory,
irradiating the openings in said metal film with a laser beam, with the scanning head and table controlled by the control part which reads the driving data from memory, thereby removing the interlayer resin layer and forming openings through which via holes are formed, and
(d) forming via holes and conductor circuits.
In order to achieve the invention""s objectives, the present invention, provides a process for producing a multi-layer printed wiring board, which comprises the following steps (a) to (h).
(a) forming an interlayer insulating resin layer on a board covered with a conductor layer,
(b) forming a metal film on said interlayer insulating resin layer,
(c) forming openings and register marks in said metal film,
(d) placing said board with said register marks on a table of an apparatus for producing a multi-layer printed wiring board, said apparatus including; an emitter of fabricating laser, a scanning head to deflect the direction of the laser beam in X-Y directions, a camera to sense the register mark on the board, a table to support the board, an entry part for entrance of data for fabricating the board, a memory to store fabricating data or computed results, and an operation part, entering processing data into said apparatus,
sensing the position of the register mark on the board by means of the camera and comparing the results of sensing with previously entered processing data, thereby generating in the operation part, data necessary to drive the scanning head, the table, and storing the data in memory,
irradiating the openings in said metal film with a laser beam, with the scanning head and table controlled by the control part which reads the driving data from memory, thereby removing the interlayer resin layer and forming openings through which via holes are formed,
(e) forming an electrolessly plated film on the board obtained in said step (d),
(f) forming a plating resist on the board obtained in said step (e),
(g) performing electrolytic plating on the part where said plating resist is not formed, and
(h) removing said plating resist and, removing by etching, the metal film and electrolessly plated film under the plating resist.
In order to achieve the invention""s objectives, the present invention, provides a process for producing a multi-layer printed wiring board, which comprises the following steps (a) to (c).
(a) forming an interlayer insulating resin layer and a metal film on a board covered with a conductor layer,
(b) forming an opening and a register mark on said metal film, and
(c) removing that part of the interlayer insulating resin layer which is exposed through the opening in said metal film, by irradiation of a laser beam aimed at the opening according to data obtained by sensing the position of the register mark, thereby forming the opening through which a via hole is formed.
In order to achieve the invention""s objectives, the present invention, provides a process for producing a multi-layer printed wiring board, which comprises the following steps (a) to (d).
(a) forming an interlayer insulating resin layer and a metal film on a board covered with a conductor layer,
(b) forming openings and register marks on said metal film,
(c) placing said board with said register marks on a table of an apparatus for producing a multi-layer printed wiring board, said apparatus including; an emitter of fabricating laser, a scanning head to deflect the direction of the laser beam in X-Y directions, a camera to sense the register mark on the board, a table to support the board, an entry part for entrance of data for fabricating the board, a memory to store fabricating data or computed results, and an operation part, entering processing data into said apparatus,
sensing the position of the register mark on the board by means of the camera and comparing the results of sensing with previously entered processing data, thereby generating in the operation part, data necessary to drive the scanning head, the table, and storing the data in memory,
irradiating the openings in said metal film with a laser beam, with the scanning head and table controlled by the control part which reads the driving data from memory, thereby removing the interlayer resin layer and forming openings through which via holes are formed, and
(d) forming via holes and conductor circuits.
The present invention according to claim 8, provides a process for producing a printed wiring board as defined in one of claims 1 to 7, wherein said register mark is an opening formed in the metal film and the sensing of said register mark is accomplished by sensing the sub-layer mark which is visible in the opening formed in said metal film through the interlayer insulating resin film.
According to the present invention, via holes are drilled in the resin insulating layer, through openings made in a metal film attached thereto, by laser irradiation directed approximately to said openings in response to the board position sensed by a camera relative to the register marks inscribed on the metal film. (This metal film functions as a resist mask for the laser beam, and it is referred to as conformal mask hereinafter.)
In this way it is possible to form via holes at adequate positions even though the accuracy of position for laser irradiation is not high, because the accuracy of the position of via holes depends solely on the accuracy of the position of the openings in the metal film (or conformal mask).
In this way it is also possible to make hundreds to thousands of via holes efficiently owing to the register marks inscribed in the metal film having openings for via holes. These register marks permit the position of the board to be determined accurately relative to the scanning head (galvano head) whose movement has already been programmed. The resulting data controls the positioning of the table and scanning head.
According to the present invention, it is possible to employ laser irradiation without sacrificing the accuracy of the position of via holes even though the board is not located very accurately. This implies that the scanning head can move faster, making more via holes per unit time, which leads to improved productivity.
In the present invention, the register marks on the multi-layer printed wiring board should ideally be inscribed on the metal film with the use of etching or the like. They may be circular, square, or rectangular in form.
Being opaque to light, the metallic register mark gives a silhouette when it is illuminated upward from the table or reflects light when it is illuminated downward. In other words, it can be recognized by the camera regardless of the direction from which it is illuminated.
The register marks should be inscribed at the same time as etching for openings on the metal film. This eliminates the necessity of performing two steps separately for making the openings and inscribing the register marks.
In another preferred embodiment, a sub-layer mark is formed on the surface of the board which is covered with an interlayer insulating resin layer and an opening (as the register mark) is formed in the metal film which functions as the conformal mask, as shown in FIGS. 11 and 12. The position is determined by sensing the sub-layer mark which is visible in the opening (or the register mark) through the resin layer. The advantage of this embodiment is that the sub-layer mark 220B, which is covered with a resin layer, does not oxidize to decrease in reflectivity, nor does it peel off (and hence it poses no problem with recognition in silhouette).
To be more concrete, the process consists of steps of forming the interlayer insulating resin layer, forming on it the metal film (which functions as the conformal mask) by physical or chemical vapor deposition or electroless plating or by hot-pressing a resin film covered with a metal film, and forming the register mark at the same time as the opening is formed by etching.
The above-mentioned interlayer insulating resin layer may be formed from a thermosetting resin or a thermoplastic resin or a combination thereof.
It may also be formed from an adhesive for electroless plating. In its most desirable form, the adhesive is composed of an uncured heat-resistant resin slightly soluble in acid or oxidizing agent and particles (dispersed therein) of a cured heat-resistant resin soluble in acid or oxidizing agent. Treatment with acid or oxidizing agent dissolves and removes the heat-resistant resin particles, thereby forming a rough surface with minute pits for anchorage.
The adhesive for electroless plating should preferably be one which contains the cured heat-resistant resin particles specified by any of the following, because it gives anchorage of a more complex structure.
(1) Heat-resistant resin particles which have an average particle diameter smaller than 10 xcexcm.
(2) Agglomerate of heat-resistant resin powder having an average particle diameter smaller than 2 xcexcm.
(3) A mixture of heat-resistant resin powder having an average particle diameter of 2-10 xcexcm and heat-resistant resin powder having an average particle diameter smaller than 2 xcexcm.
(4) Pseudo agglomerate of heat-resistant resin powder having an average particle diameter of 2-10 xcexcm, each particle of which carries on its surface heat-resistant resin powder or inorganic powder or both having an average particle diameter smaller than 2 xcexcm.
(5) A mixture of heat-resistant resin powder having an average particle diameter of 0.1-8 xcexcm and heat-resistant resin powder having an average particle diameter larger than 0.8 xcexcm and smaller than 2 xcexcm.
(6) Heat-resistant resin powder which has an average particle diameter of 0.1-10 xcexcm.
For good adhesion, the rough surface should ideally have a roughness of Rmax=0.01-20 xcexcm. In the case of semi-additive process, the preferred roughness is 0.1-5 xcexcm, which ensures good adhesion while permitting the electrolessly plated film to be removed.
The above-mentioned heat-resistant resin slightly soluble in acid or oxidizing agent should preferably be a xe2x80x9ccomposite of thermosetting resin and thermoplastic resinxe2x80x9d or a xe2x80x9ccomposite of photosensitive resin and thermoplastic resinxe2x80x9d. The former is superior in heat resistance and the latter can be applied by photolithography to form the opening for the via hole.
The above-mentioned thermosetting resin includes, for example, epoxy resin, phenol resin, and polyimide resin. These chemicals may be made photosensitive if their thermosetting groups are modified with methacrylic acid or acrylic acid. Acryl-modified epoxy resin is most suitable.
The epoxy resin includes, for example, epoxy resins of phenol novolak type or cresol novolak type and alicyclic epoxy resins formed by modification with dicyclopentadiene.
The thermoplastic resin includes, for example, polyethersulfone (PES), polysulfone (PSF), polyphenylenesulfone (PPS), polyphenylene sulfide (PPES), polyphenyl ether (PPE), polyetherimide (PI), and fluoroplastics.
The mixing ratio of the thermosetting (photosensitive) resin to the thermoplastic resin should ideally be from 95/5 to 50/50, so that the resulting compound has good toughness without a loss in heat resistance.
The amount of the heat-resistant resin particles should be 5-50 wt %, preferably 10-40 wt %, of solids in the heat-resistant resin matrix.
The heat-resistant resin particles should preferably be those of amino resin (such as melamine resin, urea resin, and guanamine resin) and epoxy resin.
Incidentally, the adhesive may be composed of two layers, each differing in composition as explained later.
Forming an interlayer insulating resin layer and a metal film simultaneously is acceptable. In this case, the board having conductor layers formed thereon is hot-pressed together with a prepreg placed thereon, said prepreg being a thermosetting resin, a thermoplastic resin, or a composite of thermosetting resin and thermoplastic resin, which is impregnated into a fibrous substrate.
The fibrous substrate may be glass cloth or aramid fiber cloth.
Another acceptable process consists of placing a metal-clad resin film on the board having conductor layers formed thereon, performing hot-pressing, thereby forming the interlayer insulating resin layer and the metal film, and etching the metal film, thereby forming the opening and register mark.
The resin film mentioned above may be of thermosetting resin, thermoplastic resin, or a composite of thermosetting resin and thermoplastic resin.
The thermosetting resin includes, for example, one or more of the following; epoxy resin, polyimide resin, phenolic resin, bismaleimide triazine resin (BT). The thermoplastic resin includes, for example, one or more of the following; polyether sulfone (PES), polyether imide (PEI), polyphenylene ether (PPE), polyphenylene sulfide (PPS), and fluoroplastics. The thermoplastic resin should be used in the form of uncured resin film.
Hot-pressing may be performed at 100-150xc2x0 C. and 5-50 kg/cm2 for thermosetting resins and 100-350xc2x0 C. and 5-100 kg/cm2 for thermoplastic resins.
The resin film should ideally be 5-100 xcexcm thick. Excessive thickness presents difficulties when hole drilling with a laser beam. Excessively thin films do not provide satisfactory interlayer insulation.
The metal film may be of one or more of the following metals; copper, nickel, aluminum, and precious metal (such as gold, silver, palladium, and platinum). Copper foil is the most desirable because of its low price and good resistance to laser beams.
The metal film should ideally be 1-20 xcexcm thick. Excessive thickness does not yield fine patterns, and excessively thin films are easily damaged by laser beams.
In a preferred embodiment of the present invention, the metal film as the conformal mask is formed by physical or chemical vapor deposition. Through this mask, openings for via holes are formed with the use of a laser. On this metal film is formed a layer by electroless plating. On this layer is formed another layer by electrolytic plating. Incidentally, the electrolessly-plated layer should be given a plating resist prior to electrolytic plating. The electrolessly-plated layer under the plating resist is removed by etching when conductor circuits and via holes are formed. The plating resist protects the electrolytically plated layer used to form conductor circuits and via holes from damage by the etching process because the metal film and electrolessly plated layer are thin enough for easy removal. Thus it is possible to create wiring with a fine pitch and via holes with an extremely small diameter. Suitable etching solutions include aqueous solution of sulfuric acid and hydrogen peroxide, aqueous solution of ammonium persulfate, and aqueous solution of ferric chloride.
The physical or chemical vapor deposition may be accomplished by sputtering or vacuum deposition.
The deposited metal film and the electrolessly-plated film covering it should preferably be thinner than 2 xcexcm. Such a thin film is easily removed by etching when conductor circuits and via holes are formed by removing unnecessary parts of the metal film and electrolessly plated layer. Therefore, the electrolytically plated layer used to form conductor circuits and via holes are not damaged by the etching process. Thus it is possible to create wiring with a fine pitch and via holes with an extremely small diameter.
In the present invention, it is permissible to form the metal film simultaneously with the interlayer insulating resin layer. This is achieved by laminating a prepreg and then performing hot pressing to cure the resin. (The prepreg is a glass fiber cloth or aramid fiber cloth impregnated with resin in B stage. A resin film may replace it in B stage.)
In this case, the steps shown in FIG. 4(D) and FIG. 5(E) are replaced by the steps shown in FIG. 9(Dxe2x80x2) and FIG. 9(Exe2x80x2).